xbill

Yet again, the fate of the world rests in your hands! An evil computer
hacker, known only by his handle 'Bill', has created the ultimate computer
virus. A virus so powerful that it has the power to transmute an ordinary
computer into a toaster oven. (oooh!) 'Bill' has cloed himslef into a
billion-jillion micro-Bills. Their sole purpose is to deliver the nefarious
virus, which has been cleverly diguised as a popular operating system.

As System Administrator/Exterminator, your job is to keep Bill from
succeeding at his task.